Wind turbines are an important technology for the generation of electricity using renewable energy resources, i.e. the wind. Their annual percentage increase in kilowatt production is currently greater than any other form of electricity-generating technology.
Presently, the most popular type of large wind turbine, i.e. greater than 25 kW (rated peak power), has a horizontal axis, referred to as a horizontal axis wind turbine (HAWT), and can have one or more high-speed, airfoil-type rotor blades used for generating lift. Wind turbines are either of variable-speed or fixed-speed type.
The kinetic energy of the wind can be expressed as: KEwind=½=mV2=½(ρAtV)V2=½ρAtV3 where m is the mass of air, ρ is the air density, A is the area swept by the wind turbine blades, t is the time, and V is the wind speed. Therefore, the power (i.e. energy/time) of the wind can be expressed as: POWERwind=½ρAV3. As we can see, the wind's power is directly related to the wind speed cubed. For example, when the wind speed doubles, its power is increased by a factor of eight (i.e. 23=8).
The power harnessed by a wind turbine is directly related to the power of the wind that passes through the area swept by the wind turbine blades.
Multiple blade wind turbines have already been previously considered. For example, U.S. Pat. No. 8,618,682 describes a looped airfoil wind turbine (LAWT) and is shown in FIGS. 1a and 1b. The LAWT is based on a conveyor-belt arrangement of horizontal airfoils. U.S. Pat. No. 7,075,191 describes a wind and water power generation device (WWPGD) using a rail system and is shown in FIG. 2. The WWPGD is based on a conveyor-belt arrangement of vertically-mounted airfoils.
U.S. Pat. No. 4,049,300 describes a fluid driven power producing apparatus (FDPPA) and is shown in FIG. 3. The FDPPA is based on a conveyor-belt arrangement of horizontally-mounted airfoils.